The present invention relates to a new and improved construction of a controlled deflection roll containing a control arrangement or control means.
Generally speaking, the controlled deflection roll equipped with a control means as contemplated by the present development is of the type comprising a roll shell which is supported by support elements upon a roll support in one or a number of effective directional planes. The support elements are distributively arranged in the direction of the lengthwise axis of the roll and can be controlled in order to influence the thereby applied support or supporting force. Also, a control arrangement is provided for adjusting the support force of the support elements, the control arrangement generating for each group of support elements a common control signal.
Controlled deflection rolls of the aforementioned type have been known to the art from, for instance, German Pat. No. 2,847,029. With the prior art controlled deflection roll there are provided a plurality of zones over the roll length, these zones in each case being supported by a group of commonly control support elements. In this way it is possible to individually alter within the separate zones the pressing force with respect to the counter element, in other words to control the roll nip or gap width.
The behaviour of such zone-controlled roll has been theoretically examined in the publication entitled "Das Papier", Volume 4, Page 125 et seq., 1980, and specifically for a three-zone roll which however is not used in actual practice. The author of such publication explains the causes for the deviations of the roll gap or nip width from a predetermined mean or average value which arise in practice; the roll profile retains its shape even in the presence of a deviating setting of the mean line force, whereas the magnitude of the deviations however vary. The aforementioned profile shape possesses in characteristic fashion so-called "null crossovers" of the gap width deviation, so that the profile assumes the known M-shape or W-shape, and there are present four null crossovers or throughpasses.
If there are increased the number of adjacently situated controlled zones, it is correspondingly possible to also increase the number of null crossovers, and there is associated therewith a reduction in the gap width deviation from the set mean or average value. However, it should be understood that an increase in the number of individually controllable zones also enlarges the structural expenditure in the equipment, since for each group of commonly control support elements there must be provided a related separate adjustment element; in the case of an adjustable roll containing hydrostatic support bearings or support elements such is constituted by a pressure control valve having its own infeed line. These infeed lines are accommodated at the roll support, which when increasing the number of infeed lines also can result in spatial problems in the design of the controlled deflection roll.